Mechanism of VEGF-Induced Uterine Venous Hyperpermeability

Abstract

Background: Transfer of molecular signals from veins to adjacent arteries is an established mechanism of vascular communication in the uterine circulation, which ultimately depends on venous permeability. This study tests the hypotheses that: (1) uterine veins are permeable to intravenous solutes, using a 3-kDa dextran tracer and (2) this permeability is enhanced in response to vascular endothelial growth factor (VEGF). Additionally, the involvement of nitric oxide (NO), calcium, and the phospholipase C-protein kinase C (PLC-PKC) cascade in VEGF-enhanced permeability were investigated, and the impact of pregnancy-induced uterine vascular remodeling on permeability was evaluated. Methods: Studies utilized fluorimetry to quantitate solute flux in isolated segments of rat uterine vein as a function of endothelial surface area and time under basal and VEGF-stimulated conditions. VEGF signaling was probed using NO synthase inhibition (L-NNA), calcium channel blockade (lanthanum chloride) and withdrawal (calcium-free solution), and inhibitors of the PLC-PKC cascade (U-73122 and chelerythrine chloride, respectively). Gestational effects were assessed using vessels from late pregnant (day 20) rats. Results: Basal flux (control) in nonpregnant animals was 26 ± 2.5 molecules/µm²/min × 1,000 and was increased significantly by VEGF in a concentration-dependent manner (1 nM ≈ 3.3-fold, 10 nM ≈ 4.6-fold). Inhibition of PLC, PKC, and calcium signaling, but not NO, attenuated the response to VEGF. Gestation significantly increased flux (78 ± 9.3 molecules/µm²/min × 1,000), and maintained responsiveness to VEGF. Conclusions: These results demonstrate uterine venous permeability to intermediate-sized solutes through a VEGF-sensitive pathway involving calcium and PLC-PKC, but not NO, and further substantiate a role for veno-arterial communication in uterine blood flow regulation during pregnancy.

Predominance of Local Over Systemic Factors in Uterine Arterial Remodeling During Pregnancy

“…Several related studies from our laboratory have shown that molecules as large as 70 kDa pass across the uterine venous wall, and that this process is augmented in pregnancy due to the increased wall tension present in the enlarged veins 28. Moreover, this process can be amplified considerably by intravenous VEGF, and is therefore subject to regulation29. Future studies will address this issue of pathway further, and at this point its involvement still remains hypothetical with regard to the circumferential remodeling of uterine artery in vivo .…”

The adaptation of the blood‐brain barrier to vascular endothelial growth factor and placental growth factor during pregnancy

“…In contrast, our results showed no increased expression of VEGFRs in the cerebral veins and also no increase in BBB permeability. This could reflect a possible protective mechanism in the brain compared to the uterine circulation that requires increased vascular permeability for controlled extravasation of intravenous molecules in the maternal-fetal unit (42), while the BBB must maintain its protective state to prevent brain edema.…”

Downstream Exposure to Growth Factors Causes Elevated Velocity and Dilation in Arteriolar Networks

“…Overall, the effective dosages causing dilation range from 10 to 1,000 p M [5,6,7,8,35,36,37,38,39]. Permeability changes and migration/proliferation effects with VEGF-A or FGF2 occur over this same range, although frequently much higher concentrations have been tested [4,34,35,40,41,42,43,44,45,46,47,48,49]. Thus, key physiological effects of growth factors (dilation, permeability, migration/proliferation) are elicited by similar concentrations in the p M range.…”

“…This value of Jv/S is of the same order of magnitude that can be found in the literature for exposure to VEGF-A (50 ng/ml or 1 n M ). Within seconds, VEGF-A increases hydraulic conductivity 2- fold [4], increases small solute (3 kD) permeability 3.3-fold [40], and in the hamster cheek pouch, large solute (150 kD) permeability is elevated as much as 10-fold at this dose [35]. Using a basal value for Lp of 2×10 –7 cm·s –1 ·cm·H 2 O –1 [4], and conservatively only doubling Lp with VEGF-A exposure to 4 × 10 –7 cm·s –1 ·cm·H 2 O –1 , at a constant net pressure of 30–50 cm H 2 O [4], Jv/S would be 6 to 10 × 10 –6 cm/s.…”